The invention relates to a safety switch.
In removing a housing or housing element of an apparatus or machine, or even for example in opening a cover or a door, it can be necessary for safety reasons to trigger a switch in an electrical circuit, particularly to interrupt and keep it interrupted as long as the door or cover is open or the housing is removed. In some such cases it is necessary to provide a forced activation of the safety switch so that the switching is assured even when the switch is damaged, for example when its contact points are welded together.
One known safety switch of the above-described type is capable of causing a forced switching, because its key, which is attached for example on the removable housing element or the door, forcibly rotates a cam disc both as it enters into the housing containing the drive and locking device and as it is pulled out thereof. The rotation of this cam disc is transformed into a forced translational movement of the switch drive member by means of a connecting rod eccentrically hinged to the cam disc. The switch drive member is connected with the other end of the connecting rod. Disadvantages of this known safety switch, however, are that the cam disc of the drive and locking device is expensive and is subject to failure because of unavoidable wear, that the connecting rod, which can have only a relatively small cross section for spacial reasons, can break when the contact points of the switch are welded together and that the disc can be rotated thereby triggering a switching step not only with the key, a projection of which engages in a notch in the outer surface of the disc, but also with a simple tool, such as a screwdriver. The latter is a significant disadvantage, since, for example, with machines, it is repeatedly attempted to operate the machine for adjustment or control purposes, when the protective hood or the like is removed, which should not be permitted for safety reasons. Furthermore, this known safety switch is neither moisture proof nor dustproof.
In West German publication DE-OS No. 2128322 there is described an electrical switch activated by a ram in which the activating force is transferred to the ram by an elastic activating lever. However, in a safety switch the activating force should not be transferred by an elastic member. For this reason alone this previously known design for a safety switch is contrary to accepted practice. The activating lever, formed of an elastic material and provided with a central longitudinal slot extending from one end nearly to the other end, can be located in various positions on the switch housing. For this reason the open-slot end section is attached to the side of the housing from which the ram extends. This attachment is accomplished with the aid of two pairs of screws, between which the free end section of the activating lever is introduced until it reaches a position in which the screws engage in notches in the activating lever. In order to activate the ram, a force must be exerted on the activating lever acting in the direction of movement of the ram. This force elastically deforms the activating lever to such an extent that the closed end section thereof comes into contact with the ram and activates same. The activating lever thus does not activate the ram of the switch as one of its ends is introduced between the screws in the manner of a key. This is another reason that this activating lever cannot be used as a key for a safety switch.